1. Field of the Invention
The present invention relates to a particle photographing device that photographs particles dispersed in a fluid, and a flow velocity measurement device that measures a flow velocity distribution in the fluid using the particle photographing device.
2. Description of the Related Art
A flow velocity measurement device that photographs tracer particles dispersed in a fluid using a particle photographing device, acquires the amount of movement of a tracer particle group based on the imaging data, and measures a flow velocity distribution in the fluid based on the amount of movement has been conventionally known (for example, see Patent Document 1).
The particle photographing device described in Patent Document 1 includes: a probe portion placed in a fluid in which particles are dispersed; an optical fiber that introduces laser light into the probe portion; and an imaging portion that images the particles in the fluid illuminated based on the laser light. The probe portion includes an illumination optical system that illuminates the particles in the fluid based on illumination light generated by diffusing, by a diffuser plate, the laser light emitted from an end position of the optical fiber. In the particle photographing device in Patent Document 1, a slit formed in the probe portion limits the photographing range of the fluid to a band-like area.
However, since the illumination light for illuminating the particles is generated by diffusing the laser light by the diffuser plate, the energy of the laser light available for illumination is lost to some extent by the diffuser plate. The particle photographing device in Patent Document 1 thus has the drawback of low illuminance of illumination light, as compared with a particle photographing device using no diffuser plate.
On the other hand, in measurement of a velocity distribution in a fluid by typical particle image velocimetry (PIV), laser light output from one end of an optical fiber is formed into sheet-like light having an appropriate thickness by an illumination optical system including a plurality of lenses, and the range illuminated by the sheet-like light is photographed. By limiting the photographing range of the fluid to a band-like area in this way, the velocity distribution can be measured accurately.